Microplastics in the air of Metro Manila, Philippines: Diurnal and seasonal dynamics and potential health risk

Microplastics (MPs) are now recognized as a component of air pollution, yet their behavior in the atmosphere-particularly in tropical cities-remains poorly understood. This study explored the diurnal and seasonal patterns of suspended atmospheric microplastics (SAMPs) in Metro Manila, Philippines. Using 24-hour active air sampling during both dry and wet seasons, the study measured concentrations, identified the dominant polymer types, and examined how these patterns relate to local weather conditions. Results showed higher SAMP levels during the dry season (0.0748 ± 0.056 MPs/m³) compared to the wet season (0.0421 ± 0.031 MPs/m³), with concentrations typically peaking during the daytime. Temperature was positively associated with SAMP levels, while humidity and rainfall correlated with lower concentrations. These patterns suggest that hot, dry conditions promote more particles remaining suspended or becoming resuspended in the air, while rain and high humidity facilitate their removal. The most common polymers detected were polyethylene terephthalate (PET) and polyester. The Polymer Hazard Index (PHI) indicated elevated environmental risk in the wet season, driven by hazardous polymers such as polyvinyl chloride (PVC) and polyurethane (PUR). Estimates suggest that people in the study area could inhale more than 130 MPs per month during the dry season. These findings provide new insight into how weather affects airborne microplastic pollution and point to the need for their inclusion in urban air quality monitoring and public health assessments.